The two-hour current affairs show, which runs from 10am to noon on weekdays, has been presented on an acting basis by Sarah McInerney since O’Rourke’s departure in May.
Byrne said that she is "truly delighted, honoured and humbled" to be taking on the role.
"My job will be to represent the voices of the RTÉ Radio 1 listeners, and to always ask the questions they want answered at this most critical time," she said following today's announcement.
"I won’t let them down. I can’t wait to get started with the legendary team who work on the show and to help craft with them, the informative, entertaining and important Today show we’ve all come to know, love and rely on in our daily listening lives."
Head of RTÉ Radio 1, Peter Woods, spoke of Byrne's previous radio experience, including presenting the Late Debate and Saturday with Claire Byrne.
"She brings that experience, a natural curiosity, focus and real integrity to the Today programme," he said.
Woods thanked McInerney “for her considerable input on this station since last May” and said he looked forward to continuing to work with her. Details of her next project will be announced in the coming weeks, RTÉ said.
